You could have such a thing occur during the mid 19th century if Sweden decides to back Denmark against Prussia.
Sweden was normally on-top in terms of military power compared to Denmark-Norway, you had instances like the Treaty of Roskilde that marked the Swedish height in terms of land area compared to Dano-Norway. Following that, you could have the second Northern War continue for longer. After the treaty of Roskilde, King Charles X continued the war but died in 1660, with the Austrian and Brandenburging armies in Pomerania, France threatened to contribute 30,000 troops to the Swedes as it viewed the invasion of Pomeranian as a breech of the peace of Westphalia. If the war kept going then you could possibly see a large if not out-right annexation of Dano-Norway as long as France keeps supporting Sweden. Other then that I can't think of any scenarios.
